Method of manufacturing a semiconductor device having a two-layered electrode structure

ABSTRACT

A terminal interconnection  45   a  including an aluminum alloy film  4   a  and a nitrogen-containing aluminum film  5   a  layered together is formed on a glass substrate  2 . Nitrogen-containing aluminum film  5   a  in a contact portion  12   a  within a contact hole  11   a  exposing the surface of terminal interconnection  45   a  has a predetermined thickness d 1  determined based on a specific resistance of the nitrogen-containing aluminum film. The thickness of the nitrogen-containing aluminum film outside the contact portion is larger than that of the nitrogen-containing aluminum film within the contact portion. Thereby, a semiconductor device or a liquid crystal display device having a reduced contact resistance and an appropriate resistance against chemical liquid is achieved.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device, a liquidcrystal display device and a method of manufacturing a semiconductordevice, and particularly relates to a semiconductor device and a liquidcrystal display device, in which a contact portion in contact with aninterconnection, an electrode or the like has a reduced contactresistance, as well as a method of manufacturing such a semiconductordevice.

2. Description of the Background Art

Liquid crystal display devices of a thin film transistor type, whichwill be referred to as “TFT-LCDs” hereinafter, have been improved toachieve larger sizes and higher definition. In accordance with this,interconnections made of alloy, which is primarily formed of aluminumand has a relatively low resistance, have been employed for preventingsignal delay on the interconnections such as a gate bus-line.

A method of manufacturing a TFT-LCD in the prior art will now bedescribed by way of example with reference to the drawings. Referring toFIG. 20, an aluminum alloy film (not shown) of about 200 nm in thicknessis formed on a surface of a glass substrate 102 by a sputtering method.A predetermined photoresist pattern (not shown) is formed on thealuminum alloy film.

Etching with etching liquid, which is primarily made of phosphoric acid,acetic acid and nitric acid, is effected on the aluminum alloy filmmasked with the photoresist pattern described above. Thereby, a gateelectrode 104 b including a gate bus-line as well as a common line 104 care formed in an image display portion A, and a terminal interconnection104 a (i.e., an interconnection 104 a on the terminal side) is formed ina terminal portion B.

Referring to FIG. 21, a silicon nitride film 106 having a thickness ofabout 400 nm is formed by a CVD method of the like on glass substrate102 so that terminal interconnection 104 a, gate electrode 104 b andcommon line 104 c are covered with silicon nitride film 106. Then, anamorphous silicon film of about 200 nm in thickness is formed on siliconnitride film 106. Further, an n⁺-type amorphous silicon film of about 50nm in thickness is formed.

A predetermined photoresist pattern (not shown) is formed on thisn⁺-type amorphous silicon film. An isotropic etching is effected on then⁺-type amorphous silicon film and the amorphous silicon film maskedwith the photoresist pattern. Thereby, amorphous silicon films 107 andn⁺-type amorphous silicon films 108 each having an isolated form areformed.

Referring to FIG. 22, a chrome film (not shown) of about 400 nm inthickness is formed by a sputtering method or the like on siliconnitride film 106 so that amorphous silicon film 107 and n⁺-typeamorphous silicon film 108 in the isolated form are covered with thischrome film. A predetermined photoresist pattern (not shown) is formedon the chrome film.

The chrome film thus masked with the photoresist pattern is etched toform drain electrodes 109 a and source electrodes 109 b. Thereafter,appropriate processing is performed to remove n⁺-type amorphous siliconfilm 108 located on each amorphous silicon film 108 which will form achannel region. Thereby, Thin Film Transistors (TFTs) T each includinggate electrode 104 b, drain electrode 109 a and source electrode 109 bare formed.

Referring to FIG. 23, a silicon nitride film 110 which covers andthereby protects thin film transistors T is formed, e.g., by the CVDmethod. A predetermined photoresist pattern (not shown) is formed onsilicon nitride film 110.

An isotropic etching is effected on silicon nitride films 110 and 106thus masked with the photoresist pattern so that contact holes 111 a areformed to expose the surfaces of drain electrodes 109 a, respectively.Contact holes 111 b are also formed for exposing the surfaces ofterminal interconnections 104 a, respectively.

Referring to FIG. 24, a transparent and conductive film made of oxidesuch as an ITO (Indium Tin Oxide) film of about 100 nm in thickness isformed on silicon nitride film 110 by the sputtering method or the likeso that contact holes 111 a and 111 b may be filled with this ITO filmor the like. A predetermined photoresist pattern (not shown) is formedon the ITO film.

The ITO film thus masked with the photoresist pattern is etched withetching liquid containing hydrochloric acid and nitric acid so thatpixel electrodes 113 a are formed in image display portion A, andterminal electrodes 113 b are formed in terminal portion B. Each pixelelectrode 113 a is electrically connected to drain electrode 109 a, ofthin film transistor T. Each terminal electrode 113 b is electricallyconnected to terminal interconnection 104 a.

Then, a glass substrate and a color filter (both not shown) are disposedon the above structure with a sealing material (not shown) therebetween.Liquid crystal is supplied into a space between glass substrate 102provided with thin film transistors T and the glass substrate coveredwith the color filter. Further, a drive IC (i.e., IC for driving) ismounted on a predetermined terminal portion. The TFT-LCD is completedthrough the manufacturing process described above.

In the TFT-LCD, as described above, alloy films primarily made ofaluminum are used in the gate bus-lines including the gate electrodes,the terminal interconnections and others. The purpose of this is toprevent signal delays by employing the alloy primarily made of aluminumas materials of the electrodes and interconnections, and therebyreducing the resistances thereof.

In the conventional TFT-LCD, however, oxide aluminum is formed on theinterface between terminal interconnection 104 a and terminal electrode113 b particularly in the contact portion within contact hole 111 b.Such oxide aluminum is probably formed, e.g., due to reaction, whichoccurs on the interface between terminal interconnection 104 a made ofthe aluminum alloy and terminal electrode 113 b made of the ITO film oranother transparent and conductive oxide film, due to oxygen plasmaprocessing after formation of the contact holes, or due to naturaloxidization occurring as a result of exposure of the substrate to theatmosphere.

Since the oxide aluminum is formed in the contact portion as describedabove, a contact resistance may take on an extremely high value of 100MΩ or more if the contact area is in a practical range. Therefore, goodelectric contact cannot be achieved between terminal electrode 113b andterminal interconnection 104 a so that the TFT-LCD cannot operateappropriately.

Further, the etching liquid, which is used for forming pixel electrode113 a and terminal electrode 113 b made of the ITO film, may spread intothe structure through pinholes in silicon nitride films 110 and 106.Since the etching liquid contains hydrochloric acid and nitric acid asalready described, terminal interconnection 104 a and gate electrode 104b made of aluminum alloy may be etched or corroded.

For overcoming the above problems, therefore, such a structure isalready proposed, e.g., in Japanese Patent Publication No. 7-113726 thata chrome film or the like is layered over the surfaces of terminalinterconnection 104 a and gate electrode 104 b made of aluminum alloy.The chrome film thus layered provides good electric connection to theITO film. Also, the chrome film has a sufficient resistance againstchemical liquid, and therefore can protect the interconnections andothers made of aluminum alloy.

For coating the surfaces of terminal interconnection 104 a and gateelectrode 104 b made of aluminum alloy with another kind of metal film,however, a sputtering device must be provided with a metal targetcorresponding to such a metal film. For forming the interconnection andothers, it is necessary to conduct different kinds of etching whichcorrespond to the film qualities of the metal films, respectively. Thisincreases the manufacturing cost, and also increases the number ofmanufacturing steps.

SUMMARY OF THE INVENTION

The invention has been developed for overcoming the foregoing problems,and first and second objects of the invention are to provide asemiconductor device and a liquid crystal display device, which areprovided with electrodes or interconnections allowing easy reduction incontact resistance and having resistances against chemical liquid. Athird object of the invention is to provide a method of manufacturingsuch a semiconductor device.

A semiconductor device according to a first aspect of the inventionincludes a substrate having a main surface, a first conductive layer anda second conductive layer. The first conductive layer is formed on themain surface of the substrate. The second conductive layer is formed onthe main surface of the substrate, and is electrically connected to thefirst conductive layer. The first conductive layer is formed of layeredfilms having a first layer primarily made of aluminum, and a secondlayer including aluminum containing nitrogen. The second layer of thefirst conductive layer and the second conductive layer are in directcontact with each other in a contact portion between the first andsecond conductive layers, and the second layer in the contact portionhas a thickness determined to provide a predetermined contact resistancebased on a specific resistance of the second layer.

According to the above structure, since the second layer of the firstconductive layer in the contact portion has the predetermined thicknessdetermined corresponding to the specific resistance value of the secondlayer, the contact resistance can be significantly reduced. As a result,the semiconductor device in which signal delay is prevented is achieved.

Preferably, the semiconductor device further includes an insulating filmformed on the substrate and covering the first conductive layer, and acontact hole formed in the insulating film and exposing the surface ofthe first conductive layer, the contact portion is located within thecontact hole, the second layer in the first conductive layer is formedon the first layer, and the second conductive layer is formed on theinsulating film and in the contact hole.

In this case, the second layer include the aluminum containing thenitrogen, and therefore can protect the first layer, e.g., from chemicalliquid such as etching liquid used for forming the second conductivelayer. Consequently, it is possible to suppress corrosion of theinterconnections and others while preventing the signal delay.

The second layer in the contact portion has the thickness d satisfying arelationship of 0<ρ·d <3Ω·μm² in the case where the specific resistanceρ of the second layer satisfies a relationship of 50<ρ≦1×10⁵ μΩ·cm, andsatisfying a relationship of 0<d<3 nm in the case where the specificresistance ρ satisfies a relationship of 1×10⁵ μΩ·cm<ρ. Thepredetermined contact resistance R preferably satisfies a relationshipof R·S<100 MΩ·μm², where S represents an area of the contact portion.Thereby, the contact resistance can be equal to 100 KΩ or less, anddesirably several kilohms when the contact area is in, a practicalrange, and therefore the contact resistance in the contact portion canbe remarkably reduced.

Preferably, the second layer outside the contact portion has thethickness T larger than that of the second layer in the contact portion.

This structure can reliably prevent chemical liquid such as etchingliquid for forming the second conductive layer from spreading into thefirst layer of the first conductive layer, e.g., through pin-holes inthe insulating film. As a result, the first conductive layer can have agood resistance against the chemical liquid.

Preferably, the crystal grain of aluminum of the first layer has asurface orientation of (111).

This structure promotes nitriding of the aluminum of the first layer,and a surface portion of the first layer having an appropriate thicknessis nitrided in the process of forming the second layer includingaluminum containing nitrogen. This improves the state of joining betweenthe first and second layers in the interface, and reduces the contactresistance.

Preferably, the thickness T of the second layer satisfies a relationshipof 0<d<20 nm in the case of the specific resistance ρ of the secondlayer satisfying a relationship of 50<ρ≦1×10^(5 μΩ·cm.)

In this case, the second layer outside the contact portion has thethickness T smaller than 20 nm. Thereby, eaves of the second layer,which is formed due to difference in film quality between the first andsecond layers during formation of the first conductive layer, can have amore gentle form. Consequently, the second conductive layer, which isformed on the first conductive layer with the insulating filmtherebetween, can be prevented from being broken on the stepped portionformed by the eaves.

In the case of the thickness T satisfying a relationship of T≧20 nm, itis preferable that the insulating film has the thickness larger than 1μm.

Owing to this increased thickness of the insulating film, it is possibleto suppress breakage of the second conductive layer even when the secondlayer forms the eaves.

The insulating film described above preferably includes a transparentresin film, and the semiconductor device can be applied, e.g., to aliquid crystal display device or the like requiring light transparency.

More preferably, the second conductive layer includes a transparentconductive film.

In this case, the semiconductor device can be applied to the liquidcrystal display device or the like.

According to a second aspect of the invention, a liquid crystal displaydevice includes a transparent substrate having a main surface, a firstconductive layer, an insulating film, a contact bole, and a transparentsecond conductive layer. The first conductive layer is formed on themain surface of the substrate. The insulating film is formed on thesubstrate and covers the first conductive layer. The contact hole isformed in the insulating film, and exposes the surface of the firstconductive layer. The second conductive layer is formed on theinsulating film, fills the contact hole, and is electrically connectedto the first conductive layer. The first conductive layer has a lowerlayer portion primarily made of aluminum, and an upper layer portionlayered on the lower layer portion and including aluminum containingnitrogen. The contact hole exposes the surface of the upper layerportion. The upper layer portion in the contact portion within thecontact hole has a thickness determined to provide a predeterminedcontact resistance based on a specific resistance value of the upperlayer portion.

According to this structure, since the upper layer portion of the firstconductive layer in the contact portion has the predetermined thicknesswhich is determined based on the specific resistance value of the upperlayer portion, the contact resistance can be significantly reduced.Since the upper layer portion includes aluminum containing nitrogen, itis possible to protect the lower layer portion from chemical liquid suchas etching liquid used for forming the second conductive layer.Consequently, it is possible to provide the liquid crystal displaydevice, in which signal delay can be easily prevented, and corrosion ofthe interconnections and others can be suppressed.

The upper layer portion in the contact portion has the thickness dsatisfying a relationship of 0<ρ·d<3Ω·μm² in the case where the specificresistance ρ of the upper layer portion satisfies a relationship of50<ρ≦1×10⁵ μΩ·cm, and satisfying a relationship of 0<d<3 nm in the casewhere the specific resistance ρ satisfies a relationship of 1×10⁵μΩ·cm<Ω. The predetermined contact resistance R preferably satisfies arelationship of R·S<100 MΩ·μm², where S represents an area of thecontact portion. Thereby, the contact resistance can be equal to 100 KΩor less when the contact area is in a practical range, and desirably isequal to several kilohms or less, and therefore the contact resistancecan be remarkably reduced.

According to a third aspect of the invention, a method of manufacturinga semiconductor device includes the following steps. Processing isperformed to form on a substrate a first conductive layer having a lowerlayer portion primarily made of aluminum, and an upper layer portionlayered on the lower layer portion and made of aluminum containingnitrogen. Processing is performed to form on the substrate an insulatingfilm covering the first conductive layer. A contact hole exposing thesurface of the upper layer portion is form:ed in the insulating film.Processing is performed to form on the insulating film a secondconductive layer electrically connected to the upper layer portionexposed on the bottom of the contact hole. In the step of forming thecontact hole, the upper layer portion in the contact portion isdetermined to have a predetermined thickness so as to provide apredetermined contact resistance based on the specific resistance valueof the upper layer portion.

According to this method, since the predetermined thickness of the upperlayer portion in the contact portion is determined based on the specificresistance of the upper layer portion in the step of forming the contacthole, the contact resistance can be significantly reduced. Since theupper layer portion includes aluminum containing nitrogen, it ispossible to protect the lower layer portion of the first conductivelayer from chemical liquid such as etching liquid used for forming thesecond conductive layer. Consequently, it is possible to manufacture thesemiconductor device, in which signal delay can be easily prevented, andcorrosion of the interconnections and others can be suppressed.

Preferably, the upper layer has the thickness d satisfying arelationship of 0<ρ·d<3Ω·μm² in the case where the specific resistance ρof the upper layer portion satisfies a relationship of 50<ρ≦1×10⁵ μΩ·cm,and satisfying a relationship of 0<d<3 nm in the case where the specificresistance ρ satisfies a relationship of 1×10⁵ μΩ·cm<ρ. Thereby, thecontact resistance can be equal to 100 KΩ or less when the contact areais in a practical range, and desirably is equal to several kilohms orless, and therefore the contact resistance can be remarkably reduced.

Preferably, the upper layer portion is formed in a nitrogen atmosphereby a sputtering method under the conditions of 0.1<F/D<10 ml/nm where Frepresents a flow rate of the nitrogen supplied into the atmosphere incontact with the substrate, and D represents a growth rate of the upperlayer portion (conditions of 0.1<F/D ≦10 ml/nm will be referred to asconditions A, and conditions of 1<F/D<10 ml/nm will be referred to asconditions B, hereinafter).

Under the above conditions A, the upper layer portion has a relativelylow specific resistance, and the predetermined contact resistance can beachieved while keeping a large margin of the thickness of the upperlayer portion. Under the conditions B, the upper layer portion has arelative high specific resistance, and a resistance can be kept againstchemical liquid such etching liquid, e.g., for forming the secondconductive layer.

Under the conditions A described above, since the margin of thethickness of the upper layer portion is large, it is preferable that thegrowth rate D of the upper layer portion satisfies a relationship of3<D<60 nm/min.

Under the conditions B, however, the specific resistance is relativelyhigh so that the thickness achieving the predetermined contactresistance can be selected only from a relatively narrow range. In thiscase, the growth rate D of the upper layer portion preferably satisfiesa relationship of 3<D<10 nm/min.

Preferably, formation of the lower layer portion starts after thepressure decreases to or below 10⁻³ Pa.

This feature can remarkably suppress formation of aluminum oxide betweenthe lower and upper layer portions.

Preferably, the substrate is exposed to an atmosphere containing oxygenin a concentration of 10⁻¹⁰ mol/l or less for a period from start offormation of the lower layer portion to end of formation of the upperlayer portion.

In this case, it is likewise possible to suppress reliably the formationof aluminum oxygen between the lower and upper layer portions.

Preferably, the upper layer portion is formed in an atmospherecontaining a nitriding gas nitriding aluminum. The nitriding gas maypreferably contain a gas containing at least one of nitrogen, ammonia,hydrazine and hydrazone.

Preferably, a scan magnetron sputtering device is used for the firstconductive layer.

According to the scan magnetron sputtering device, a distribution ofthickness of the first conductive layer formed on the substrate can becontrolled by an oscillating speed of a magnet, and therefore thethickness of the first conductive layer within the surface of thesubstrate can be easily controlled.

Preferably, the step of forming the contact hole includes supply of anitriding gas nitriding aluminum before the lower layer portion isexposed.

In this case, even when the etching for forming the contact hole removesthe upper layer portion to expose the surface of the lower layerportion, a nitrogen-containing aluminum film is formed at the surface ofthe lower layer portion owing to the supply of the nitriding gas.Thereby, increase in the contact resistance can be suppressed.

Preferably, the step of forming the first conductive layer includes astep of patterning the first conductive layer by dry etching.

In this case, it is possible to eliminate eaves of the upper layerportion, which may be caused due to difference in film quality betweenthe upper and lower layer portions, in contrast to the case ofperforming wet etching for patterning. As a result, the secondconductive layer formed on the first conductive layer can be preventedfrom being broken on a stepped portion of the first conductive layer.

It is desired that the nitrogen used as the nitrifying gas is in advancemixed and diluted with an inert gas within a gas cylinder.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section showing a first step in a method ofmanufacturing a liquid crystal display device according to a firstembodiment of the invention;

FIG. 2 is a cross section showing a step performed after the step shownin FIG. 1 according to the first embodiment;

FIG. 3 is a cross section showing a step performed after the step shownin FIG. 2 according to the first embodiment;

FIG. 4 is a cross section showing a step performed after the step shownin FIG. 3 according to the first embodiment;

FIG. 5 is a cross section showing a step performed after the step shownin FIG. 4 according to the first embodiment;

FIG. 6 is a fragmentary cross section showing, on an enlarged scale, astep performed after the step shown in FIG. 5 according to the firstembodiment;

FIG. 7 is a cross section showing a step performed after the step shownin FIG. 5 according to the first embodiment;

FIG. 8 is a cross section showing a step performed after the step shownin FIG. 7 according to the first embodiment;

FIG. 9 is a cross section showing a step performed after the step shownin FIG. 8 according to the first embodiment;

FIG. 10 is a graph showing a distribution of contact resistance withrespect to the thickness of a nitrogen-containing aluminum film and aspecific resistance according to the first embodiment;

FIG. 11 is a fragmentary cross section showing, on an enlarged scale, astep performed in a method of manufacturing a liquid crystal displaydevice according to a second embodiment of the invention;

FIG. 12 is a fragmentary cross section showing, on an enlarged scale, astep performed in a method of manufacturing a liquid crystal displaydevice according to a third embodiment of the invention;

FIG. 13 is a cross section showing a step performed in a method ofmanufacturing a liquid crystal display device according to a fourthembodiment;

FIG. 14 is a cross section showing a step performed after the step shownin FIG. 13 according to the fourth embodiment;

FIG. 15 is a cross section showing a step performed after the step shownin FIG. 14 according to the fourth embodiment;

FIG. 16 is a fragmentary cross section showing, on an enlarged scale,the step shown in FIG. 15 according to the fourth embodiment;

FIG. 17 is another fragmentary cross section showing, on an enlargedscale, the step shown in FIG. 15 according to the fourth embodiment;

FIG. 18 is a cross section showing a step performed after the step shownin FIG. 15 according to the fourth embodiment;

FIG. 19 is a fragmentary cross section showing, on an enlarged scale, anadvantage of the liquid crystal display device according to the fourthembodiment;

FIG. 20 is a cross section showing a step in a method of manufacturing aliquid crystal display device in the prior art;

FIG. 21 is a cross section showing a step performed after the step shownin FIG. 20;

FIG. 22 is a cross section showing a step performed after the step shownin FIG. 21;

FIG. 23 is a cross section showing a step performed after the step shownin FIG. 22; and

FIG. 24 is a cross section showing a step performed after the step shownin FIG. 23.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

A liquid crystal display device according to a first embodiment of theinvention will now be described. First, a manufacturing method will bedescribed below with reference to the drawings. Referring to FIG. 1, atarget material of aluminum alloy is sputtered onto a glass substrate 2,which has an image display portion A and a terminal portion B, in achamber of a scan magnetron sputtering device (which will be referred toas a “sputtering device” hereinafter) so that an aluminum alloy film 4having a thickness of about 200 nm and containing, e.g., 0.2 wt% ofcopper is formed on glass substrate 2.

Glass substrate 2 is kept within the chamber, and a target material ofaluminum alloy is sputtered while supplying a nitrogen gas diluted withan argon gas into the chamber. Thereby, a nitrogen-containing aluminumfilm 5 (i.e., aluminum film 5 containing nitrogen) is formed on aluminumalloy film 4.

Nitrogen-containing aluminum film 5 is formed under the followingconditions. The sputtering device has a DC power of 1 KW. A dilutednitrogen gas which is a gas mixture of argon (Ar) and 10% of N₂contained in a gas cylinder is used as the nitrogen gas to be suppliedinto the chamber. The flow rate of this gas mixture is equal to 50 sccm.Thus, a net flow rate F of the nitrogen gas is equal to 5 sccm. The filmforming or depositing time is controlled so that nitrogen-containingaluminum film 5 may have a thickness of about 12 nm, and control is alsoperformed to grow nitrogen-containing aluminum film 5 at a growth rate Dof about 20 nm/min.

The formation of nitrogen-containing aluminum film 5 starts when thepressure in the chamber which is not yet supplied with the gas mixturedecreases to 10⁻³ Pa or less. The concentration of oxygen in the chamberis kept at 10⁻¹⁰ mol/l or less for a period after the start of formationof aluminum alloy film 4 to the end of formation of nitrogen-containingaluminum film 5.

Referring to FIG. 2, a predetermined photoresist pattern (not shown) isformed on nitrogen-containing aluminum film 5. Using the photoresistpattern as a mask, etching is effected on nitrogen-containing aluminumfilm 5 and aluminum alloy film 4 with etching liquid primarily made ofphosphoric acid, acetic acid and nitric acid so that gate electrodes 45b each including a gate bus-line as well as common lines 45 c are formedin image display portion A. Also, terminal interconnections 45 a (i.e.,interconnections 45 a on the terminal side) are formed in terminalportion B. Thereafter, the photoresist pattern is removed.

Referring to FIG. 3, a silicon nitride film 6 of about 400 nm inthickness is formed, e.g., by a plasma CVD method over terminalinterconnections 45 a, gate electrodes 45 b and common lines 45 c.Subsequently, an amorphous silicon film of about 200 nm in thickness isformed. Further, an n⁺-amorphous silicon film of about 50 nm inthickness is formed.

A predetermined photoresist pattern (not shown) is formed on then⁺-amorphous silicon film. Using the photoresist pattern as a mask,etching is effected on the n⁺-amorphous silicon film and the amorphoussilicon film so that amorphous silicon films 7 and n⁺-amorphous siliconfilms 8 each taking the isolated form are formed. Each amorphous siliconfilm 7 in the isolated form will form a channel portion of a thin filmtransistor which will be completed later.

Referring to FIG. 4, a chrome film (not shown) of about 400 nm inthickness is formed by a sputtering method over each amorphous siliconfilm 7 and n⁺-amorphous silicon film 8 in the isolated form. Apredetermined photoresist pattern (not shown) is formed on this chromefilm.

Using the photoresist pattern as a mask, etching is effected on thechrome film to form drain electrodes 9 a and source electrodes 9 b.Then, dry etching is effected to remove n⁺-amorphous silicon film 8 oneach channel region. Thereafter, the photoresist pattern is removed.Thereby, thin film transistors T each including gate electrode 45 b,drain electrode 9 a and source electrode 9 b is formed.

Referring to FIG. 5, a silicon nitride film 10 covering each thin filmtransistor T is formed on silicon nitride film 6 by the CVD method orthe like. A predetermined photoresist pattern (not shown) is formed onsilicon nitride film 10.

Using the photoresist pattern as a mask, anisotropic etching is effectedon silicon nitride films 10 and 6 to form contact holes 11 a eachexposing the surface of drain electrode 9 a and contact holes 11 b eachexposing the surface of terminal interconnection 45 a.

This anisotropic etching is performed with an etching gas containing CF₄or SF₆. The overetching is performed at a rate of about 30%. This valueis determined for preventing such a disadvantage particularly in contacthole 11 b that the thickness of nitrogen-containing aluminum film 5exposed on the bottom of contact hole 11 b is reduced below the intendedrange due to the overetching.

In this step, as shown in FIG. 6, nitrogen-containing aluminum film 5 ain a contact portion 12 a within contact hole 11 b has a thickness d₁ ofa predetermined value, which is determined to provide a predeterminedcontact resistance in accordance with a value of a specific resistanceof nitrogen-containing aluminum film 5 a, as will be described later.

Referring to FIG. 7, a sputtering method or the like is performed toform an ITO film (not shown) of about 100 nm in thickness, which fillscontact holes 11 a and 11 b, on silicon nitride film 10. A predeterminedphotoresist pattern is formed on this ITO film.

The ITO film thus masked with the photoresist pattern is etched withetching liquid containing hydrochloric acid and nitric acid so thatpixel electrodes 13 a are formed in image display portion A. Also,terminal electrodes 13 b are formed in terminal portion B. Each pixelelectrode 13 a is electrically connected to source electrode 9 a.Terminal electrode 13 b is electrically connected to terminalinterconnection 45 a.

For stabilizing the characteristics of thin film transistor T, annealingis performed at a temperature from 130° C. to 300° C. This annealingtemperature affects the contact resistance in the contact portion, andtherefore it is important to avoid excessive increase in annealingtemperature. In this embodiment, the annealing temperature is 250° C.

Referring to FIG. 8, an orientation film 15 covering pixel electrode 13a is formed on silicon nitride film 10. A glass substrate 17 is arrangedon glass substrate 2 provided with orientation film 15 with a sealingmember 16 therebetween. Glass substrate 17 is already provided with acolor member 18, a black matrix 19, an ITO film 20 and an orientationfilm 21.

Liquid crystal 22 is supplied into a space between orientation films 15and 21. Then, as shown in FIG. 9, a drive IC substrate 24 carrying driveICs (i.e., ICs for drive) is mounted on a liquid crystal panel 23. DriveIC substrate 24 and liquid crystal panel 23 are electrically connectedtogether by a flexible printed circuit 25. Through the steps describedabove, the liquid crystal display device provided with liquid crystalpanel 23 is completed.

According to the liquid crystal display device thus formed, sincenitrogen-containing aluminum film 5 a of a predetermined thickness ispresent on the interface between terminal electrode 13 b formed of theITO film and terminal interconnection 45 a, the contact resistance canbe significantly reduced.

This will be described below in greater detail. FIG. 10 shows a resultof evaluation relating to the contact resistance of the contact portionin the contact hole having a size of 35 μm square, and particularly aresult of evaluation of the dependency of the above contact resistanceon the thickness of the nitrogen-containing aluminum film and thespecific resistance thereof. In FIG. 10, blank circles represent pointswhere the contact resistance is lower than 500 Ω. Hatched circlesrepresent points where the contact resistance is in a range between 500Ω to 100 KΩ. Solid circles represent points where the contact resistanceis larger than 100 kΩ.

According to the results of measurement in FIG. 10, a blank region(region A) in FIG. 10 represents a region where the contact resistance Ris relatively low (R≦500 Ω). A closely hatched region B represents aregion where the contact resistance is between 500 Ω and 100 KΩ. Acoarsely hatched region C represent a region where the contactresistance is larger than 100 KΩ.

The contact resistance is desirably 100 KΩ or less, and more desirably500 Ω or less. Therefore, it has been found that the thickness andspecific resistance of nitrogen-containing aluminum film 5 must bedetermined to be within the region A or B.

More specifically, it has been found that the thickness d of thenitrogen-containing aluminum film is merely required to satisfy arelationship of 0<ρ·d<3Ω·μm² in the case where a specific resistance ρof nitrogen-containing aluminum film 5 satisfies a relationship of50<ρ≦1×10⁵ μΩ·cm.

Also, it has been found that the thickness d of the nitrogen-containingaluminum film is merely required to satisfy a relationship of 0<d<3 nmin the case where specific resistance ρ of the nitrogen-containingaluminum film satisfies a relationship of 1×10⁵ μΩ·cm<ρ.

The above range of the thickness can provide a desired contactresistance even if the value of specific resistance ρ increases to about1×10¹⁰ μΩ·cm, and this is already confirmed by an experiment.

FIG. 10 shows the results in the case where the contact hole has a sizeof 35 μm square. However, it has been found that contact resistance R ismerely required to satisfy a relationship of R·S<100 MΩ·μm² where Srepresents an area of the contact portion.

Thereby, the contact resistance can be set to 100 KΩ or less, anddesirably several kilohms when the contact area is of a practical value.By setting the thickness of the nitrogen-containing aluminum film in thecontact portion to the foregoing value, it is possible to reduceremarkably the contact resistance in the contact portion betweenterminal interconnection 45 a and terminal electrode 13 b. As a result,signal delay in the liquid crystal display device can be prevented.

The above result can be utilized for the nitrogen-containing aluminumfilm remaining in the contact portion after formation of the contacthole. Thereby, results similar to those shown in FIG. 10 can be probablyachieved even in connection with contact resistances of contact holeshaving different sizes.

In this liquid crystal display device, nitrogen-containing aluminum film5 is layered on aluminum alloy film 4 of terminal interconnection 45 a.This structure can prevent etching and corrosion of aluminum alloy film4, e.g., by etching liquid during formation of pixel electrode 13 a andterminal electrode 13 b.

According to this embodiment, conditions for forming nitrogen-containingaluminum film 5 are determined so that nitrogen flow rate F and filmgrowth rate D may satisfy a relationship of (F/D=0.25 ml/nm (F/D=0.025ml/Å).

Particularly, nitrogen-containing aluminum film 5 which is formed withF/D ranging from 0.1 to 1 ml/nm (0.01-0.1 ml/Å) has a relatively lowspecific resistance. As the specific resistance of nitrogen-containingaluminum film 5 lowers, the thickness can be increased while achieving agood contact resistance, as can be seen from FIG. 10.

Accordingly, a high accuracy of the thickness is not required in theplane of glass substrate 2 when forming nitrogen-containing aluminumfilm 5 on glass substrate 2. When the value of F/D is in the foregoingrange, the specific resistance of the nitrogen-containing aluminum filmtakes on the value of about 500 μΩ·cm, and the contact resistance takeson the value of 500 Ω or less when the nitrogen-containing aluminum filmhas a thickness in a practical range from about several nanometers toabout 100 nanometers.

The thickness of nitrogen-containing aluminum film 5 layered on aluminumalloy film 4 is determined as follows.

First, the nitrogen-containing aluminum film is etched by an amount from5 to 10 nm due to dry etching performed for forming contact hole 11 bshown in FIG. 5 or 6. This amount of etching is taken into considerationso that thickness d₁ of nitrogen-containing aluminum film 12 in contactportion 12 a may fall within an intended range shown in FIG. 10.

Consideration is given to a form or configuration of patterning ofterminal interconnection 45 a and gate electrode 45 d including the gatebus-line. An eaves of the nitrogen-containing aluminum film may beformed in the step shown in FIG. 2 for patterning nitrogen-containingaluminum film 5 and aluminum alloy film 4 by wet etching. This eaves isformed due to film quantities and, more specifically, a difference inetching rate between nitrogen-containing aluminum film 5 and aluminumalloy film 4.

In this case, the eaves of the nitrogen-containing aluminum film can bereduced by minimizing the thickness of nitrogen-containing aluminum film5, e.g., to 20 nm or less.

Taking this into consideration, the thickness of nitrogen-containingaluminum film 5 is set, e.g., to about 12 nm. With this value ofthickness, a product of specific resistance ρ of the nitrogen-containingaluminum and thickness d of the nitrogen-containing aluminum film doesnot fall outside a range of 0<ρ·d <3Ω·μm² even when the thickness of thenitrogen-containing aluminum film and/or the value of specificresistance, e.g., in a peripheral portion of glass substrate 2 deviatefrom the target values, respectively. Thereby, the contact resistancevalue in the contact portion can be set to a relatively low value of 100KΩ or less, and more preferably 500 Ω or less.

The eaves of the nitrogen-containing aluminum film is further reduced,and therefore it is possible to prevent breakage of pixel electrode 13 aand others formed on the stepped portion, e.g., of gate electrode 45 b.

The process described above was used for manufacturing a liquid crystaldisplay device. Thereby, it was found that a reduced contact resistancecan be easily achieved between a transparent electrode such as terminalelectrode 13 b and an aluminum alloy interconnection of, e.g., terminalinterconnection 45 a, of which stable formation is impossible inmass-production processes, e.g., of large liquid crystal displaydevices. Further, liquid crystal display devices having large screenssuch as 15-inch or more diagonal screens can be stably manufacturedthrough a process requiring an extremely small number of photoengravingsteps.

The process described above can be applied not only to large liquidcrystal display devices but also to mid-sized liquid crystal displaydevices with 15-inch or less diagonal screens, which can be manufacturedby preparing multiple substrates from a large substrate. As comparedwith high-melting-point metal which has been used as materials ofinterconnections and electrodes in the prior art, the target loaded inthe sputtering device can be inexpensive owing to use of aluminum alloy,and therefore a manufacturing cost can be reduced. The etching liquidfor patterning aluminum alloy film and others is inexpensive, which alsoallows reduction in manufacturing cost.

In all the liquid crystal display devices each including a dividedsubstrate produced from the large single substrate, good contactresistances can be stably achieved, and therefore a productivity can beimproved.

In the process of forming aluminum alloy film 4 and nitrogen-containingaluminum film 5, it is desired to take the following measures forsuppressing formation of a coating film of aluminum oxide over aluminumalloy film 4.

It is desired that the concentration of oxygen in the chamber is kept at10⁻¹⁰ mol/l or less for a period from the start of formation of aluminumalloy film 4 to the end of formation of nitrogen-containing aluminumfilm 5.

It is desired that the nitrogen-containing aluminum film is formedwithout supplying an atmospheric air into the chamber after the pressureof 10⁻¹⁰ Pa or less is set in the chamber before formation of thenitrogen-containing aluminum film.

Particularly, it is desired to use a scan magnetron sputtering devicefor uniformly forming the nitrogen-containing aluminum film on thesurface of glass substrate 2. In this case, it is desired that thegrowth rate of the nitrogen-containing aluminum film is in a range from3 to 60 nm/min to allow at least multiple times of scanning by a magnetin the scan magnetron sputtering device so that the thickness of thenitrogen-containing aluminum film may fall within a range from 5 to 20nm. The growth rate in this range allows uniform distributions of thethickness and quality within glass substrate 2.

By using the nitrogen gas which is already mixed and diluted uniformlywith an argon gas in a gas cylinder, the nitrogen can be uniformlysupplied to the surface of glass substrate 2 in the chamber in spite ofthe fact that the flow rate of nitrogen is extremely small. This allowsprecise control of an extent to which sputtered aluminum particles arenitrided, and therefore can improve the uniformity in specificresistance of nitrogen-containing aluminum film 2 on the plane of glasssubstrate 2.

The above embodiment has been described in connected with the case wherenitrogen-containing aluminum film 5 has a relatively low resistance(about 1×10⁵ μΩ·cm or less). Even in the case where thenitrogen-containing aluminum film having the specific resistance largerthan that described above is to be formed, a good contact resistance canlikewise be achieved by providing the nitrogen-containing aluminum filmof the thickness of about 3 nm or less in the contact portion as shownin FIG. 10.

The nitrogen-containing aluminum film having a relatively high specificresistance can be formed by setting a ratio F/D between nitrogen flowrate F and film growth rate D to a value within a range from 1 to 10ml/nm (0.1-1 ml/Å). More specifically, the nitrogen-containing aluminumfilm having a relatively high specific resistance can be formed by thesputtering method performed under the conditions where a DC power is 1KW, and a flow rate of the gas mixture of argon and nitrogen is 150 sccm(net flow rate F of the nitrogen gas is 15 sccm). In this case, thenitrogen-containing aluminum film grows at growth rate D of about 7nm/min. The film forming time is controlled to provide thenitrogen-containing aluminum film of about 7 nm in thickness.

If the specific resistance is relatively high, the thickness which canachieve the good contact resistance in the contact portion is restrictedin a considerably narrow range. Therefore, it is necessary from thestart of processing to control the thickness of the nitrogen-containingaluminum film on the plane of glass substrate 2 with an accuracy of ±1nm. For achieving this accuracy, it is desired that the film growth rateof the nitrogen-containing aluminum film is in a range from 3 to 10nm/min.

In this case, it is necessary to control the amount of etching of thenitrogen-containing aluminum film, which is caused by the dry etchingfor forming the contact hole, and more specifically to control thisetched amount to a value from 4 to 6 nm. Therefore, it is necessary toreduce thicknesses of silicon nitride film 6 forming the gate insulatingfilm and silicon nitride film 10 forming the interlayer insulating film.

Since the nitrogen-containing aluminum film has the further reducedthickness of about 7 nm, it is possible to prevent substantially aninfluence by the eaves of the nitrogen-containing aluminum film, whichoccurs due to wet etching for patterning terminal interconnection 45 aand gate electrode 45 b.

This embodiment employs the nitrogen gas for forming nitrogen-containingaluminum film 5. However, a gas other than the nitrogen gas can be used,and more specifically, a gas of at least one of ammonia, hydrazine andhydrazone may be used provided that it is a nitriding gas capable ofnitriding aluminum.

For providing the uniform thickness and uniform specific resistance ofthe nitrogen-containing aluminum film in the plane of glass substrate 2,a target of aluminum which contains nitrogen may be loaded in thesputtering device for forming the nitrogen-containing aluminum film. Inthis case, a flow of the nitriding gas already described may be suppliedso that the nitrogen-containing aluminum film formed on glass substrate2 can be compensated for lack of nitrogen (N), and it is possible toprovide nitrogen-containing aluminum film 5 having the specificresistance close to the specific resistance of the target material.

Instead of forming nitrogen-containing aluminum film 5 on aluminum alloyfilm 4, the nitrogen-containing aluminum film may be formed by nitridingthe surface of aluminum alloy film 4.

For example, a nitriding gas such as a gas of nitrogen, ammonia,hydrazine or hydrazone is supplied into the chamber after formation ofaluminum alloy film 4, and annealing is performed at-a temperature of100° C. or more so that the nitrogen-containing aluminum film is formedat the surface of aluminum alloy film 4.

By generating plasma from the nitrogen gas, a nitriding speed of thealuminum alloy film can be increased, and the nitrogen-containingaluminum film can be formed within a further reduced time.

In the foregoing methods, the concentration of oxygen in the chamber isset to 10⁻¹⁰ mol/l or less, and the substrate is transported between thechambers through a preliminary chamber in which the pressure in thesputtering device is equal to 10⁻³ Pa or less. Thereby, theconcentration of oxygen to which the substrate is exposed can be kept at10⁻¹⁰ mol/l or less for a period from the start of formation of thealuminum film to the end of formation of the nitrogen-containingaluminum film.

The crystal grain of aluminum alloy film 4 may have a surfaceorientation of (111). This promotes nitriding of the aluminum, and thealuminum alloy film can be nitrided through an appropriate thicknessbefore formation of the nitrogen-containing aluminum film. This improvesa joining state of the interface between nitrogen-containing aluminumfilm 5 and aluminum alloy film 4, and therefore can reduce the contactresistance.

The nitrogen-containing aluminum film may be a nitrided aluminum film,which is an example of a compound of the aluminum and the nitrogen. Inaddition to this, similar effects are probably achieved by an aluminumfilm, in which nitrogen is solely present in the aluminum film, as wellas a film such as a nitrogen-containing aluminum film, in which nitrogenis solely present in the film.

Second Embodiment

In the foregoing liquid crystal display device according to the firstembodiment, the nitrogen-containing aluminum film formed on the aluminumalloy film is relatively thin. A liquid crystal display device accordingto a second embodiment, which will now be, described, employs thenitrogen-containing aluminum film which is relatively thick.

First, a manufacturing method will be described. Steps similar to thosein the first embodiment, which are described with reference to FIG. 1,are conducted to form aluminum film 4 and nitrogen-containing aluminumfilm 5 on glass substrate 2.

In the above process, nitrogen-containing aluminum film 5 is formedunder the following conditions. The sputtering device has a DC power of1 KW. A diluted nitrogen gas which is a gas mixture of argon (Ar) and20% of N₂ contained in a gas cylinder is used as the nitrogen gas to besupplied into the chamber. The flow rate of this gas mixture is equal to50 sccm. Thus, a net flow rate F of the nitrogen gas is equal to 10sccm. The film forming or depositing time is controlled to increase thethickness of nitrogen-containing aluminum film 5 to about 25 nm.Thereby, the nitrogen-containing aluminum film having a relatively highspecific resistance (1×10⁵ μΩ·cm or less) is formed.

The aluminum alloy film is made of aluminum alloy, e.g., containing 0.2wt% of copper.

Thereafter, steps similar to those in the first embodiment shown inFIGS. 2 to 4 are conducted, and silicon nitride film 10 covering thinfilm transistor T is formed by a step similar to that shown in FIG. 5.

Anisotropic etching is effected on silicon nitride films 10 and 6 maskedwith a predetermined photoresist pattern so that contact holes 11 a and11 b are formed. In this processing, a gas mixture of CF₄ and ° 2 or agas mixture of SF₆ and O₂ is used as an etching gas.

In this step, as shown in FIG. 11, the rate of overetching is set to125% in view of the initial thickness (25 nm) of the nitrogen-containingaluminum film and its etching rate of about 5 nm/min so that thenitrogen-containing aluminum film in contact portion 12 a may have apredetermined thickness d₂ when forming contact hole 11 b. Thereby, thenitrogen-containing aluminum film in contact portion 12 a can have athickness d₂ of about 10 nm.

Then, steps similar to those employed in the first embodiment and shownin FIGS. 7 to 9 are conducted so that the liquid crystal display deviceis completed.

According to the liquid crystal display device thus manufactured,thickness d₂ of nitrogen-containing aluminum film 5 contact portion 12 ais set to the predetermined value in accordance with the value ofspecific resistance of nitrogen-containing aluminum film 5.

If nitrogen-containing aluminum film 5 has thickness d₂ of about 10 nm,nitrogen-containing aluminum film 5 has the specific resistance of about1×10⁵ μΩ·cm or less, and the contact resistance in contact portion 12can be set to a relatively low preferable value not exceeding 100 KΩ andmore preferably not exceeding 500 Ω as shown in FIG. 10. Thereby, signaldelay can be prevented similarly to the liquid crystal display device ofthe first embodiment.

In addition to the effects which can be achieved by the liquid crystaldisplay device of the first embodiment, the liquid crystal displaydevice of the second embodiment can achieve the following effects.

According to the liquid crystal display device of the second embodiment,the nitrogen-containing aluminum film outside the contact portion has athickness larger than that (about 12 nm) of the nitrogen-containingaluminum film in the liquid crystal display device of the firstembodiment. Therefore, even if chemical liquid such as etching liquidused for forming pixel electrode 13 a and terminal electrode 13 bspreads through contact holes in silicon nitride films 10 and 6, theliquid can be reliably prevented from reaching aluminum alloy film 4.

As a result, etching and/or corrosion of terminal interconnection 45 aand gate electrode 45 b including the gate bus-line can be reliablyprevented.

Third Embodiment

A liquid crystal display device according to a third embodiment will nowbe described. The following liquid crystal display device according tothe third embodiment employs the nitrogen-containing aluminum film,which is relatively thick, and has a relatively high specificresistance.

Steps similar to those, which are employed in the first embodiment andare described with reference to FIG. 1, are conducted to form aluminumfilm 4 and nitrogen-containing aluminum film 5 on glass substrate 2.

In the above process, nitrogen-containing aluminum film 5 is formedunder the following conditions. The sputtering device-has a DC power of1 KW. A diluted nitrogen gas which is a gas mixture of argon (Ar) and20% of N₂ contained in a gas cylinder is used as the nitrogen gas to besupplied into the chamber. The flow rate of this gas mixture is equal to50 sccm. Thus, net flow rate F of the nitrogen gas is equal to 10 sccm.The film forming time is controlled to increase the thickness ofnitrogen-containing aluminum film 5 to about 20 nm. Thereby, thenitrogen-containing aluminum film having a relatively high specificresistance (1×10⁵μΩ·cm or less) is formed.

The aluminum alloy film is made of aluminum alloy containing, e.g., 0.2wt% of copper.

Thereafter, steps similar to those in the first embodiment shown inFIGS. 2 to 4 are conducted, and silicon nitride film 10 covering thinfilm transistor T is formed by a step similar to that shown in FIG. 5.

Anisotropic etching is effected on silicon nitride films 10 and 6 maskedwith a predetermined photoresist pattern so that contact holes 11 a and11 b are formed.

For forming contact holes 11 a and 11 b, etching is effected in twosteps.

In the first etching, a gas mixture of CF₄ and O₂ or a gas mixture ofSF₆ and O₂ is used, and overetching at a rate of about 125% is effected.Thereafter, supply of O₂ gas is stopped, and N₂ gas is supplied.

In the second etching, a gas mixture of CF₄ and N₂ or a gas mixture ofSF₆ and N₂ is used, and etching is performed for about 50 seconds.

In the above manner, the oxygen gas is stopped, and the nitrogen gas issupplied before the surface of aluminum alloy film 4 is exposed byetching of nitrogen-containing aluminum film 5. Therefore, such asituation is prevented that the subsequently exposed surface of aluminumalloy film 4 is subjected to the oxygen (O₂) to form a coating film ofaluminum oxide. Thus, the aluminum layer containing the nitrogen isformed on the surface of aluminum alloy film 4.

Then, steps similar to those employed in the first embodiment and shownin FIGS. 7 to 9 are conducted so that the liquid crystal display deviceis completed.

According to the manufacturing method, as shown in FIG. 12, thenitrogen-containing aluminum film of a desired thickness can be easilyformed in contact portion 12 a owing to the etching performed in twosteps even in such a case that the uniformity of nitrogen-containingaluminum film 5 on glass substrate 2 is not good, and control ofthickness d₃ in the contact portion is difficult.

More specifically, even if the surface of aluminum alloy film 4 ispartially exposed on the bottom of contact hole 11 b during formation ofcontact hole 11 b by the etching, the nitrogen-containing aluminum filmhaving an expected thickness from 2 to 4 nm is formed on the exposedsurface because the oxygen gas is stopped, and the nitrogen gas issupplied before the surface of aluminum alloy film 4 is exposed.

As a result, the good contact resistance can be achieved in contactportion 12 a, and signal delay can be prevented similarly to the liquidcrystal display device of the first embodiment.

In the liquid crystal display device of this embodiment, thenitrogen-containing aluminum film outside contact portion 12 a has athickness larger than that (about 12 nm) of the nitrogen-containingaluminum film in the liquid crystal display device of the firstembodiment.

Similarly to the liquid crystal display device of the second embodiment,therefore, etching and/or corrosion of terminal interconnection 45 a andgate electrode 45 b including the gate bus-line can be reliablyprevented.

Fourth Embodiment

A liquid crystal display device according to the fourth embodiment ofthe invention will now be described. In the liquid crystal displaydevices of the first to third embodiments, layered structures eachincluding the aluminum alloy film and the nitrogen-containing aluminumfilm are employed as the terminal interconnections and gate electrodes.In the liquid crystal display device of this embodiment, layeredstructures each including the aluminum alloy film and thenitrogen-containing aluminum film are employed also as the sourceelectrode and the drain electrode of the thin film transistor, as willbe described below.

Steps similar to those in the first embodiment shown in FIGS. 1 to 3 areperformed, and then a chrome film 31 of about 100 nm in thickness isformed by the sputtering method as shown in FIG. 13. An aluminum alloyfilm 32 of about 200 nm in thickness is formed by the sputtering methodover chrome film 31. Further, a nitrogen-containing aluminum film 33 isformed on aluminum alloy film 32.

In the above process, nitrogen-containing aluminum film 33 is formedunder the following conditions. The sputtering device has a DC power of1 KW. A diluted nitrogen gas which is a gas mixture of argon (Ar) and10% of N₂ contained in a gas cylinder is used as the nitrogen gas to besupplied into the chamber. The flow rate of this gas mixture is equal to50 sccm. Thus, net flow rate F of the nitrogen gas is equal to 5 sccm.Growth rate of the nitrogen-containing aluminum film is set to about 20nm/min. The film forming time is controlled to increase the thickness ofnitrogen-containing aluminum film 5 to about 30 nm.

Aluminum alloy film 32 is made of aluminum alloy containing, e.g., 0.2wt% of copper.

Then, a photoresist pattern (not shown) is formed on nitrogen-containingaluminum film 33. Using the photoresist pattern as a mask, etching iseffected on nitrogen-containing aluminum film 33 and aluminum alloy film32, and further etching is effected on chrome film 31.

Then, dry etching is effected to remove n⁺-type amorphous silicon film 8on the channel region so that source electrodes 9 a including the sourceinterconnection and drain electrodes 9 b are formed as shown in FIG. 14.Thereafter, the photoresist pattern is removed.

Referring to FIG. 15, silicon nitride film 10 is formed by the CVDmethod or the like on silicon nitride film 6 for protecting thin filmtransistors T. A photosensitive transparent resin film 34, which has athickness of about 3 μm and is made of, e.g., acrylic resin, is appliedonto silicon nitride film 10.

Then, photoengraving is conducted to etch photosensitive transparentresin film 34 and silicon nitride films. 10 and 6, whereby contact holes11 a and 11 b are formed. An etching gas for this etching is made of CF₄or SF₆. The overetching rate is equal to about 30%. The purpose of thisis to prevent such a situation that the overetching reduces thethickness of the nitrogen-containing aluminum film in the contactportion to a value below a desired value.

In contact hole 11 a through which the surface of source electrode 9 ais exposed, nitrogen-containing aluminum film 33 a is etched afteretching of silicon nitride film 10 in contrast to contact hole 11 b.Therefore, the nitrogen-containing aluminum film in contact hole 11 a isetched by a thickness larger than that by which nitrogen-containingaluminum film 5 a is etched in contact hole 11 b.

In this case, as shown in FIGS. 16 and 17, the thickness ofnitrogen-containing aluminum film 33 is determined to be larger by about30 nm than that of nitrogen-containing aluminum film 5. Thereby,nitrogen-containing aluminum film 33 a in the contact portion withincontact hole 11 a can have a desired thickness. This will be describedlater in greater detail.

Referring to FIG. 18, an ITO film (not shown) of about 100 nm inthickness is formed, e.g., by the sputtering method on photosensitivetransparent resin film 34 including contact holes 11 a and 11 b. Apredetermined photoresist pattern (not shown) is formed on this ITOfilm.

Etching is effected on the ITO film thus masked with the photoresistpattern to form pixel electrodes 13 a and terminal electrodes 13 b.Thereafter, steps similar to those of the first embodiment shown inFIGS. 8 and 9 are performed so that the liquid crystal display device iscompleted.

The manufacturing method described above provides thenitrogen-containing aluminum film having desired thicknesses inrespective contact portions 12 a and 12 b within contact holes 11 a and11 b shown in FIGS. 16 and 17.

In contact hole 11 b, the silicon nitride films are etched by athickness of about 500 nm in total (silicon nitride film 6 is etched by400 nm, and silicon nitride film 10 is etched by 100 nm). This etchingcauses overetching of 30%. As a whole, therefore, the etching reduces athickness of about 650 nm in terms of thickness of the silicon nitridefilm, and the thickness reduced by the overetching corresponds to about150 nm.

In contact hole 11 a, the silicon nitride film is etched by a thicknessof about 100 nm in total (silicon nitride film 10 is etched by 100 nm).This etching reduces a thickness of about 650 nm in terms of thicknessof the silicon nitride film, and the thickness reduced by theoveretching corresponds to about 550 nm.

Assuming that an etching selection ratio (AIN/SiN) between thenitrogen-containing aluminum film and the silicon nitride film is equalto about 1/20, nitrogen-containing aluminum film 5 a in contact hole 11b is etched by about 7.5 nm. Since the initial thickness ofnitrogen-containing aluminum film 5 a is about 12 nm, anitrogen-containing aluminum film d₄ of about 4.5 nm in thickness isleft when the etching ends.

In contact hole 11 a, nitrogen-containing aluminum film 33 a is etchedby about 27.5 nm. Since the initial thickness of nitrogen-containingaluminum film 33 a is about 30 nm, a nitrogen-containing aluminum filmd₅ of about 2.5 nm in thickness is left when the etching ends.

In this manner, the nitrogen-containing aluminum films can have thethicknesses which provide desired contact resistance values in contactportions 12 a and 12 b, respectively.

The liquid crystal display device described above employs photosensitivetransparent resin film 34 of about 1 μm or more in thickness. Ifphotosensitive transparent resin film 34 is not employed, etching forforming source electrode 19 a and drain electrode 9 b causes a largeeaves 41 of nitrogen-containing aluminum film 33 a as shown in FIG. 19because the nitrogen-containing aluminum film has a relatively largethickness of 20 nm or more.

Therefore, as depicted within a circle 42 of dotted line in FIG. 19,eaves 41 may cause breakage of pixel electrode 13 a, which is made of anITO film and is formed on the stepped portion of source electrode 9 a.

According to the liquid crystal display device, since the photosensitivetransparent resin film 34 is formed as described above, it can provide aflat surface on which pixel electrode 13 a and others are formed, andbreakage of pixel electrode 13 a can be prevented.

If the dry etching is employed instead of the wet etching for formingsource electrode 9 a and drain electrode 9 b, formation of the eaves ofnitrogen-containing aluminum film 33 a can be prevented. In this case,photosensitive transparent resin film 34 can be eliminated.

The dry etching described above can be performed, e.g., under thefollowing conditions. Reactive Ion Etching (RIE) is employed, andchlorine (Cl₂) and boron trichloride (BCl₃) are used as the etching gas.The pressure in the chamber is set to 10 Pa. The RF power is 1500 W. Theetching time is 120 seconds.

Similar etching may be employed for forming the gate electrodesincluding the gate bus-lines in the liquid crystal display devices ofthe respective embodiments already described. Thereby, the eaves of thenitrogen-containing aluminum film is not formed even if thenitrogen-containing aluminum film has a thickness of 20 nm or more, andtherefore the margin of the initial thickness of the gate bus-line canbe increased. Further, a resistance of the interconnections againstchemical liquid can be improved by increasing the thickness of thenitrogen-containing aluminum film.

By employing the photosensitive transparent resin film, a parasiticcapacitance between pixel electrode 13 a and drain electrode 9 a can bereduced, and such a structure can be employed that pixel electrode 13 aoverlaps with drain electrode 9 a including the drain interconnection.

Thereby, the source interconnection covers widthwise an insufficientlyoriented region around pixel electrode 13 a, and a numerical aperture ofthe liquid crystal display device panel can be improved. The numericalaperture is a ratio between a region where a black matrix 19 shown inFIG. 8 and interconnections intercept the light and a region throughwhich light can pass.

By using aluminum alloy having a relatively low resistance, eachinterconnection width can be reduced in design, and thereby thenumerical aperture can be further increased.

Each of the foregoing embodiments has been described in connection withthe liquid crystal display device using the amorphous silicon thin filmtransistors of the channel etching type. However, the aluminum alloyfilm and the nitrogen-containing aluminum film can be applied to thesource interconnections of the liquid crystal display device using lowtemperature polycrystalline silicon thin film transistors of a planartype. Thereby, similar effects can be achieved.

In addition to the liquid crystal display devices, various kinds ofsemiconductor devices having multi-layer interconnection structurescontaining aluminum alloy may employ the contact portions, in which thenitrogen-containing aluminum films have predetermined thicknesses,respectively, whereby semiconductor devices having low contactresistances can be achieved.

The contact portions located in the contact holes have been described byway of example. In addition to this, the foregoing structure can beapplied to a portion where two interconnections are in electricalcontact so that the contact resistance can be significantly reduced.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by a the terms ofthe appended claims.

What is claimed is:
 1. A method of manufacturing a semiconductor devicecomprising the steps of: forming on a substrate a first conductive layerhaving a lower layer portion primarily made of aluminum, and an upperlayer portion layered on said lower layer portion and made of aluminumcontaining nitrogen; forming on said substrate an insulating filmcovering said first conductive layer; forming a contact hole exposing acontact surface of said upper layer portion in said insulating film; andforming on said insulating film a second conductive layer electricallyconnected to said contact surface; the upper layer portion within saidcontact hole being determined to have a thickness so as to provide adesired con tact resistance based on the specific resistance value ofsaid upper layer portion in said step of forming said contact hole. 2.The method of manufacturing the semiconductor device according to claim1, wherein said upper layer portion has the thickness d satisfying arelationship of: 0<ρ·d<3Ω·μm²  in the case where the specific resistanceρ of said upper layer portion satisfies a relationship of 50<ρ≦1×10⁵μΩ·cm, and satisfying a relationship of: 0<d<3 nm  in the case wheresaid specific resistance ρ satisfies a relationship of 1×10⁵ μΩ·cm<ρ;and said predetermined contact resistance R satisfies a relationship of:R·S<100 MΩ·μm² where S represents an area of said contact portion. 3.The method of manufacturing the semiconductor device according to claim2, wherein said upper layer portion is formed in a nitrogen atmosphereby a sputtering method under the conditions of: 0.1<F/D<10 ml/nm  whereF represents a flow rate of the nitrogen supplied into the atmosphere incontact with said substrate, and D represents a growth rate of saidupper layer portion.
 4. The method of manufacturing the semiconductordevice according to claim 3, wherein said growth rate D satisfies arelationship of: 3<D<60 nm/min  in the case of 0.1<F/D≦1 ml/nm, andsatisfies a relationship of: 3<D<10 nm/min  in the case of 1<F/D≦10ml/nm.
 5. The method of manufacturing the semiconductor device accordingto claim 1, wherein formation of said lower layer portion starts afterthe pressure of an atmosphere in contact with said substrate decreasesto or below 10⁻³ Pa.
 6. The method of manufacturing the semiconductordevice according to claim 1, wherein a concentration of oxygen containedin an atmosphere in contact with said substrate is 10⁻¹⁰ mol/l or lessfor a period from start of formation of said lower layer portion to endof formation of said upper layer portion.
 7. The method of manufacturingthe semiconductor device according to claim 1, wherein said upper layerportion is formed in an atmosphere containing a nitriding gas.
 8. Themethod of manufacturing the semiconductor device according to claim 1,wherein said step of forming said contact hole includes supply of anitriding gas before said lower layer portion is exposed.
 9. The methodof manufacturing the semiconductor device according to claim 1, whereinsaid step of forming said first conductive layer includes a step ofpatterning said first conductive layer by dry etching.
 10. The method ofmanufacturing the semiconductor device according to claim 1, wherein thestep of forming a contact hole comprises forming a reduced thicknesssection of said upper layer portion.